On Thursday Kayak Software (NASDAQ:KYAK) surprised investors by agreeing to be sold to Priceline.com (NASDAQ:PCLN) for $40 a share just months after a July initial public offering. As tech investors took in the news Groupon's (NASDAQ:GRPN) bigger-than-expected third-quarter loss pushed shares in the daily deals giant to all-time lows. The two announcements shouldn't be seen in isolation. Tech investors should take Kayak Software and Groupon's diverging fortunes as a lesson in how to discriminate between business models that work and those that are still unproven. The comparison highlights that a focused excellence wins out over revenue growth or scale ...